The disclosure generally relates to a communication system and, more particularly, to transmissions of uplink control information in a communication system.
In the mobile communication system, the user equipment (UE) needs to report multiple types of information to the base stations for enhancing the communication quality. For example, in the 3rd Generation Partnership Project (3GPP) specification, the UE may report, the sounding reference signal (SRS) and several types of uplink control information (UCI), e.g., the channel status information (CSI) and the scheduling request (SR).
Other techniques are also utilized in the advanced communication standards for further improving the communication performance. For example, by utilizing the traffic adaptation mechanism, the base station may utilize the data frame with a suitable uplink-downlink (UL-DL) configuration for flexibly adjusting the subframes used for uplink and downlink services.
For a time division duplexing (TDD) communication system, the UL-DL configuration of the legacy UE may be changed according to the system information transmitted by the base station, e.g., the System Information Block Type 1 (SIB1) transmitted by the evolved NB (eNB) in 3GPP long-term evolution (LTE) system. In the 3GPP LTE system, the minimum period of transmitting the SIB1 is usually long (e.g., 640 ms) and the legacy UE may only change the UL-DL configuration with a time equal to or longer than the minimum period of transmitting the SIB1. This semi-static resource allocation may not adapt to fast varying traffic characteristics and environments of the communication channels, and the system performance may be seriously deteriorated.
Thus, dynamically allocating the UL-DL configuration with a shorter period (e.g., less than 640 ms of the minimum period of transmitting the SIB1) is proposed for improving the system performance. Other problems, however, arise accompanied with the newly adopted techniques. For example, when the traffic adaptation mechanism is utilized, the UE may need to timely and frequently report the UCI so that the base station may have better understanding about the situation of the communication channels. The uplink resources are often limited and traditional UCI reporting mechanisms therefore cannot handle with the rapidly changing situation of the communication channels. Especially, the problem is more complicated when smaller ranged base stations are adopted, e.g., microcell base stations and femtocell base stations.